reserve fi,psi for Ordinal-Sequence,
  A,A1,B,C,D for Ordinal,
  X,Y for set,
  x,y for object;

theorem
  A in B implies A in B+^C & A in C+^B
proof
  assume
A1: A in B;
A2: B c= C+^B by Th24;
  B c= B+^C by Th24;
  hence thesis by A1,A2;
end;
